An imager used to take pictures of the retina is known as a fundus camera. These cameras could be used in fundus (retinal) photography and fluorescence angiography procedure. The latter is a retinal examination procedure where fluorescein dye is injected into a patient vein and a fundus camera is used to record images of the retina to reveal retinal blood circulation disorders, such as leakages, hemorrhages, edema and other pathologies.
Roughly speaking, there are two kinds of fundus cameras: mydriatic fundus cameras utilizing continuous illumination of the retina with visible light to permit focusing and non-mydriatic fundus cameras utilizing illumination of is the retina with invisible light, such as infrared light, which advantageously is not seen by the patient and therefore does not cause the contraction of the iris during the alignment procedure. Non-mydriatic cameras can be used in cases where dilation of the eye is not possible or in cases, such as screening of the retina, since in those cases following the positioning using invisible light a single high-intensity image of higher illumination (usually white) intensity is used per each patient eye. With the mydriatic fundus camera approach, it is necessary to apply a pupil-dilating (mydriatic) medication to the cornea in order to avoid contraction of the pupil in response to visible light to enable full visualization of the entire retina throughout the clinical procedure. In the non-mydriatic fundus camera, which allows focus on the retina in the naturally dilated state of the pupil, the eye is illuminated by infrared light and a continuous image is formed on an infrared imaging device or the light sensing plane of an infrared sensor such as a CCD or CMOS video camera.
The presently available high-performance fundus cameras typically use Halogen illumination or Xenon-Flash light to obtain various white light, single wavelength light (Red, Green, and Blue—using filters), fluorescein (FA) and Indo-Cyanine Green (ICG or ICGA) fluorescence images.
Clinically, there is a need to follow the fluorescence process throughout the life-cycle of the fluorescence agent, and especially during the initial phase of the agent entering the retinal and choroidal blood circulation. Due to the limitation of current technology in fundus cameras, only 1 or 2 Xenon-flash based images per second are possible to obtain, because of limitations of the energy sources to the Flash devices. Only laser beam based scanning devices (known also as SLO—Scanning Laser Opthalmoscopes) are able to record such events, with the limitation of smear and motion of the eye during image acquisition, causing limitation in image quality of the retina image.
Various techniques have been developed aimed at improving the performance of a fundus camera. For example, U.S. Pat. No. 5,742,374 discloses a fundus camera for photographing fundus of an eye to be examined. According to this technique, an observing illumination/target projection optical system utilizes a slit-plate having a pin-hole aperture and a ring-slit. The eye to be examined is illuminated with a ring-slit illumination to facilitate alignment and focusing.
The use of LED based illumination in a fundus camera has been proposed, and is described in U.S. Pat. No. 6,685,317. Here, a digital camera is described that combines the functions of the retinal camera and corneal camera into one, single, small, easy-to-use instrument. The single camera can acquire digital images of a retinal region of an eye, and digital images of a corneal region of the eye. The camera includes a first combination of optical elements for making said retinal digital images, and a second combination of optical elements for making said corneal digital images. In a preferred embodiment, a portion of these elements are shared elements including a first objective element of an objective lens combination, a digital image sensor and at least one eyepiece for viewing either the retina or the cornea. Also, preferably, the retinal combination also includes a first changeable element of said objective lens system for focusing, in combination with said first objective element, portions or all of said retinal region at or approximately at a common image plane. Also, preferably, the retinal combination also includes a retinal illuminating light source, an aperture within said frame and positioned within said first combination to form an effective retinal aperture located at or approximately at the lens of the eye defining an effective retinal aperture position, an infrared camera for determining eye position, and an aperture adjustment mechanism for adjusting the effective retinal aperture based on position signals from said infrared camera. Also, preferably, the cornea combination of elements includes a second changeable element of said objective lens system for focusing, in combination with said first objective element, portions or all of said cornea region at or approximately at a common image plane.
According to the technique of U.S. Pat. No. 6,685,317, light from a large area is collected by a fiber optic bundle. High power LEDs emit over a wide angle typically ±90 degrees. However, it appears that the optical setup described in this patent suffers inter alia from losing the majority of light due to the very small acceptance angle of commercially available fibers.